The present invention relates to an internal combustion engine that forms a swirl effect in a combustion chamber, where an intake port pointing toward the outer perimeter of the combustion chamber is disposed on one side of the upper surface of the combustion chamber. More specifically, the present invention relates to a piston used in this type of internal combustion engine.
In internal combustion engines, it has been known that generating a swirl effect in the combustion chamber can promote fuel mixing and flame propagation, thus improving combustion. For this reason, various means for creating swirl effects have been considered. In one example, an intake passage opening that guides intake air into a combustion chamber, i.e. an intake port, is positioned away from the center of the combustion chamber and is pointed toward the outer perimeter.
Also, internal combustion engines need to have the intake air concentrated near the ignition point of the spark plug. This is achieved by having a cavity formed on the end surface of the piston under the ignition point of the spark plug and by having a projection disposed on another section of the end surface. The projection generally extends laterally across the end surface of the piston so that it separates the intake port from the exhaust port, and is disposed near a section of the end surface that faces the intake port.
However, when a piston having this kind of projection is used with an internal combustion engine that creates the swirling described above, the projection obstructs the flow of the intake air coming into the combustion chamber from the intake port. This disrupts the flow and prevents a strong swirl effect from being created.
In Japanese Laid-Open Publication Number 62-178717, there is disclosed a piston having a projection disposed on the end surface of the piston. The projection is similar to the projection described above although it serves a different purpose. A cut-away section is formed on the projection at a position facing the intake port. A concave groove extending laterally is disposed on the end surface of the piston and is interposed between the section facing the intake port and the section facing the exhaust port. The cut-away section described above is directly continuous with this concave groove.
In internal combustion engines having this kind of piston, the intake air coming in from the intake port flows into the concave groove via the cut-away section of the projection. Thus, the projection is prevented from obstructing the flow of intake air. As a result, a swirl effect is created in the combustion space formed by the concave groove.
However, when a cut-away directly connected to the concave groove is formed in this manner on the projection on the piston end surface, the cut-away is positioned in the path of the swirling formed in the concave groove. Thus, the swirl that was generated is weakened by the cut-away.